[SPARK-33269][INFRA] Ignore ".bsp/" directory in Git

### What changes were proposed in this pull request?

After SBT upgrade into 1.4.0 and above. there is always a ".bsp" directory after sbt starts:
https://github.com/sbt/sbt/releases/tag/v1.4.0
This PR is to put the directory in to `.gitignore`.

### Why are the changes needed?

The ".bsp" directory is an untracked file for git during development. This is annoying.

### Does this PR introduce _any_ user-facing change?

No

### How was this patch tested?

Manual local test

Closes apache#30171 from gengliangwang/ignoreBSP.

Authored-by: Gengliang Wang <[email protected]>
Signed-off-by: HyukjinKwon <[email protected]>

.gitignore

@@ -8,6 +8,7 @@
 *.swp
 *~
 .DS_Store
+.bsp/
 .cache
 .classpath
 .ensime